This invention relates to an improvement of a spark plug for an internal combustion engine.
Various kinds of spark plugs have been provided hitherto in which the standard spark plug now in use in most of cars has a ground electrode rectangular-shape in cross section. The ground electrode is welded to the upper end of a cylindrical outer metal part of the plug and is bent such that the free end portion thereof becomes substantially parallel to the terminal end of the central electrode.
In an internal combustion engine, when ignition of the combustible gases occurs with such standard spark plug, the burning gases are forcibly ejected from the area of the spark, and they are ejected away from the plug in straight paths. This straight movement of the burning gases (flame front) will normally continue in the direction it is ejected from the spark plug area, but will divert in various directions as it meets non-combustible areas of gas, and will follow a path of the most highly combustible gases. This means that although the gas was ejected in a straight path from the spark plug, this path will consist of a series of diverted paths away from the initial direction.
When the flame front of the burning gases meets the cylinder walls and top of the piston, it will then be reflected in various directions, depending on the shape of the surface it strikes, and will be set into a form of swirling action. However, as the speed of the flame front has considerably reduced by this time, the degree of swirling action developed as a result of the shape of the cylinder (combustion chamber) walls and the piston top is accordingly less intense, and quickly dissipates so that little of this swirling action is residual by the time the next intake of combustible gas and firing occurs.
Another factor is that the electrode causes a "shadow" in the flame front. That is the burning gases being ejected away from the spark plug, and being in a straight path, do not swirl around the back of the electrode, and a shadow is left. This can be compared with a beam of light and an object placed in the path of the light beam, immediately behind the object there is almost no light, and this dark area is termed a shadow. In the case of the standard spark plug electrode, this area of shadow behind the electrode becomes a delayed firing area and causes irregularities in the smooth burning and resulting power available from the combustion of the fuel.
Also, in an internal combustion engine, the piston on the upward exhaust stroke causes the burnt gas from the combustion of the fuel to be pushed (exhausted) out of the cylinder through the open exhaust valve. However, the elimination of all burnt gas from the cylinder is not possible because the piston does not fully contact the cylinder top, and there is always a space between the top of the piston and the top of the cylinder when the piston is at the maximum upward position. Therefore, there is always this residual amount of burnt (non-combustible) gas remaining in the cylinder.
When the piston goes into the intake stroke and draws the fuel and air mixture into the cylinder, this residual non-combustible gas partly mixes with the combustible fuel and air mixture. However, some pockets or areas of the non-combustible gas remain unmixed with the combustible mixture. When the piston comes up to the compression stroke for firing of the fuel at the top of the stroke when the fuel is compressed, the combustible mixture of fuel and air is ignited by the spark plug. If the combustible mixture of fuel and air is surrounding and in the gap of the spark plug when the spark is caused to occur across the gap, ignition of the fuel and air mixture will be immediate. However, as explained above there are some remaining pockets of almost only the residual non-combustible gas, and if this pocket of non-combustible gas is in the spark gap or in the immediate vicinity, ignition of the combustible mixture of fuel and air will not occur because it is isolated from the spark by the area of non-combustible gas, and accordingly a misfire or late fire will occur.
The above described condition occurs mostly at low engine speeds when the movement of gases within the cylinder is relatively slow and the mixing of the residual non-combustible gas with the combustible fuel and air mixture is only partial. Many methods have been devised to overcome this problem, such as specially designed shapes of the top of the cylinder and the piston head. The positioning of the exhaust valve and the intake valve also play an important part in endeavours to overcome this problem. Some of these methods have provided improvement but have not completely solved the problem. Therefore, even in the most effectively designed engine the effect of the residual non-combustible gas still shows up as unstable engine speeds and irregular firing at low engine speeds, and especially so at idle speeds.
The inventor has been aware of this condition for a considerable time, and during the progress of research on the development of low pollution carburetors found this problem becoming increasingly more troublesome as the optimum mixture of fuel and air for low pollution combustion was approached. This unstable firing condition became a barrier to the final approach of low pollution without the use of catalysts, etc. As a result of investigations into this problem it became apparent that the residual non-combustible gas must be kept away from the area of the spark plug or be thoroughly mixed by some means with the combustible mixture of fuel and air, and by such mixing the effect of irregular firing would be eliminated.
Accordingly, an object of the present invention is to provide a spark plug which allows the smooth burning of an air and fuel mixture without causing a substantial shadow in the flame front in the combustion chamber.
Another object of the present invention is to provide a spark plug which causes an integral mixing of the non-combustible residual gases in the combustion chamber with the new charge of combustible fuel and air mixture and thereby provides regular and even firing of the new fuel/air charge.
A further object of the present invention is to provide a spark plug which causes an increase of power of an engine with less consumption of the fuel.
A still another object of the present invention is to provide a spark plug which is easily adapted to almost all internal combustion engines now in use.
A further object of the present invention is to provide a spark plug which is simple in structure and inexpensive to manufacture.